Some httpc requests neither complete nor trigger error - concurrency

Question

This Erlang based web client issues N concurrent requests to a given URL, e.g., escript client.erl http://127.0.0.1:1234/random?num=1000 3200 issues 3200 concurrent requests. For completeness, a corresponding server can be found here.
The client uses spawn_link to spawn N processes to issue one request each. The success/failure of httpc:request call in the spawned process is handled in the spawned process (within the dispatch_requests function) and propagated to the parent process. The parent process also handles both data messages from a spawned process and EXIT messages corresponding to the abnormal termination of a spawned process. So, the parent process waits to receive N messages from/about the spawned processes before it terminates normally.
Given the above context, the client hangs on some executions (e.g., the server is terminated forcefully) as the parent process never receives N messages from the children processes. I am observing this behavior on Raspberry Pi 3B running Raspbian 9.9 and esl-erlang 22.0-1.
The parent process does not seem to be not handling all cases of termination of child processes. If so, what are these cases? If not, what might be the reason for fewer than N messages?
Client code:
% escript client.erl http://127.0.0.1:1234/random?num=5 30
-module(client).
-export([main/1]).
-import(httpc, [request/1]).
-mode(compile).
dispatch_request(Url, Parent) ->
Start = erlang:monotonic_time(microsecond),
{Status, Value} = httpc:request(get, {Url, []}, [{timeout, 60000}], []),
Elapsed_Time = (erlang:monotonic_time(microsecond) - Start) / 1000,
Msg = case Status of
ok ->
io_lib:format("~pms OK", [Elapsed_Time]);
error ->
io_lib:format("~pms REQ_ERR ~p", [Elapsed_Time, element(1, Value)])
end,
Parent ! {Status, Msg}.
wait_on_children(0, NumOfSucc, NumOfFail) ->
io:format("Success: ~p~n", [NumOfSucc]),
io:format("Failure: ~p~n", [NumOfFail]);
wait_on_children(Num, NumOfSucc, NumOfFail) ->
receive
{'EXIT', ChildPid, {ErrorCode, _}} ->
io:format("Child ~p crashed ~p~n", [ChildPid, ErrorCode]),
wait_on_children(Num - 1, NumOfSucc, NumOfFail);
{Verdict, Msg} ->
io:format("~s~n", [Msg]),
case Verdict of
ok -> wait_on_children(Num - 1, NumOfSucc + 1, NumOfFail);
error -> wait_on_children(Num - 1, NumOfSucc, NumOfFail + 1)
end
end.
main(Args) ->
inets:start(),
Url = lists:nth(1, Args),
Num = list_to_integer(lists:nth(2, Args)),
Parent = self(),
process_flag(trap_exit, true),
[spawn_link(fun() -> dispatch_request(Url, Parent) end) ||
_ <- lists:seq(1, Num)],
wait_on_children(Num, 0, 0).